1. Field of the Invention
The present invention relates to a differential apparatus for a vehicle and an assembling method thereof, and more particularly relates to a differential apparatus for a vehicle and an assembling method thereof having pinion gear supporting portions preventing pinion gears from inclining.
2. Description of the Related Art
It is well known for this kind of the differential apparatus for the vehicle as shown in a prior art as disclosed in a document of a registered utility model No. 2520728.
The prior art of the differential apparatus for the vehicle will be explained hereinafter referred to FIG. 1. In FIG. 1, the differential apparatus 71 for the vehicle includes a differential case 72 rotated by receiving torque from an engine, a pair of side gears 73R, 73L installed in parallel each other along a rotational axis of the differential case 72, and a pinion gear 74 engaging with the side gears 73R, 73L.
The differential case 72 has an accommodating space 72A accommodating the pair of side gears 73R, 73L and the pinion gear 74. In the differential case 72 are mounted a pinion gear inserting hole 75 communicating with the accommodating space 72A and inserting the pinion gear 74 therethrough and also mounted a pair of tire shaft inserted holes 76R, 76L opened to a direction perpendicular to an axis of the pinion gear inserting hole 75.
The pair of side gears 73R, 73L are hollow cylindrical bevel gears having boss portions 79R, 79L and gear portions 80R, 80L to be installed movably along the rotational axis of the differential case 72. The pair of side gears 73R, 73L are rotatably supported in the differential case 72 in the way that the boss portions 79R, 79L face to the tire shaft inserted holes 76R, 76L respectively. With an inside surface of each of the side gears 73R, 73L is engaged a part of each of right and left tire shafts 81R, 81L inserted into each of tire shaft inserted holes 76R, 76L. Annular sliding members 82R, 82L are inserted between back surfaces of the gear portions 80R, 80L of the side gears 73R, 73L and inner opened peripheral edges of the shaft inserted holes 76R, 76L.
The pinion gear 74 is a hollow cylindrical bevel gear held by a pinion gear stopper 83 and is rotatably supported in a pinion gear inserting hole 75. At a center axis portion of the pinion gear 74 is mounted a shaft penetrating hole 74A penetrated by a pinion gear shaft 84 for preventing the pinion gear from inclining.
Upon the construction of the prior differential apparatus for the vehicle, when torque from the engine of the vehicle is input to the differential case 72 through the drive pinion and the ring gear, the differential case 72 is rotated around the rotating axis. Upon the rotation of the differential case 72, rotational force is transferred to the pinion gears 74 through the pinion gear shaft 84 and to the side gears 73R, 73L through the pinion gears 74. Because the right and left side gears 73R, 73L are engaged with the tire shafts 81R, 81L in spline fitting respectively, torque from the engine is transmitted to the right and left tire shafts through the drive pinion, the ring gear, the differential case 72, the pinion gear shaft 84, the pinion gears 74, the side gears 73R, 73L.
In this case, since the pinion gear 74 slides on each of the supporting surfaces of the pinion gear inserting hole 75 and the pinion gear shaft 84 upon the rotation of the pinion gear 74, frictional resistance is generated between the pinion gear 74 and each of the supporting surfaces, thereby to restrict the differential rotation of the side gears 73R, 73L.
And also, since thrust force is generated at engaging surfaces of the pinion gear 74 with the side gears 73R, 73L upon the rotation of pinion gear 74, the side gears 73R, 73L are moved to be separated each other by the thrust force to press the sliding member 82R, 82L to the inner opened peripheral edges of the tire shaft inserted holes 76R, 76L so that another frictional resistance is generated between the sliding member 82R, 82L and the tire shaft inserted holes 76R, 76L, thereby restricting the differential rotation of the side gears 73R, 73L.
However, in the prior art of the differential device for the vehicle disclosed in the registered utility model document, there happen next wrong phenomena. The pinion gear supporting surface of the pinion gear 74 includes a first sliding portion formed with a circular peripheral portion at a back surface of the pinion gear 74, that is at end face far from the rotational axis of the differential case 72 of both opposite ends of the pinion gear 74 along its axial direction, and a second sliding portion formed with a part of an outer peripheral surface of the gear portion engaging with the side gears 73R, 73L at near to the rotational axis of the differential case in comparison that the first sliding portion is. Therefore, the engaging area between the inner surface of the pinion gear inserting hole 75 and the second sliding portion upon the rotational phase of the pinion gear 74 so that there is no stable differential restricting torque and a size of engaging area of the pinion gear 74 can not be set as enough large size, thereby it is not able to achieve high flexibility of setting a higher torque bias ratio TBR.